Add Support For Module Containers as Iterables (#28255)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28255
Add support for treating Sequentials, ModuleLists, and ModuleDicts as iterables.
As previously, when emitting a for loop over a Module Container we unroll the for loop over all elements. We require that any Sugared Value in an iterable with a Module Container have a statically - determinable length.
Otherwise, if you zipped over a list of varying length and an nn.Sequential that alternated between returning a Tensor and a Dictionary, the output type would change based on the length of the list.
Fix for #17179
And https://github.com/pytorch/pytorch/issues/27401
and https://github.com/pytorch/pytorch/issues/27506
Test Plan: Imported from OSS
Reviewed By: ZolotukhinM
Differential Revision: D18278124
Pulled By: eellison
fbshipit-source-id: aca336a5b8da89c756b1f0884883649510cbde3c
